<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
    /**
        id不能重复 - 规范
     */
    #first {
        color: red;
    }

</style>
<body>
    你好
    <div>111</div>
    <h1 class="p1 p2">标题哦</h1>
    <p>段落哦</p>
    <p id="first" class="p1 p2">段落哦1</p>
</body>
</html>